The main purpose of this proposal is to define the mechanism of immunologic enhancement with the aid of an experimental model developed in this laboratory. In this model, suppression of delayed hypersensitivity to purified protein antigens develops at the time of appearance of circulating antibody. Studies will be initiated to determine the relative roles of T-cells and B-cells in this suppression. With the aid of blastogenesis, the effect of this suppression on the antigen reactive cell will be investigated. The changes in affinity of the antigen-binding cells will be measured at different phases of the delayed response. The influence of different classes of immunoglobulins on the suppressed state will also be studied. The regulation of the extent of delayed hypersensitivity will be attempted by sensitization with antigen-antibody complxes in different ratios.